, these vaccines may generate potent neutralizing antibodies with strong protective immunity against viral infection. S1 subunit, for example, is much shorter than the full-length S protein, but it is no less able to induce strong immune responses and/or protection against viral infection (Li et al., 2013; Adney et al., 2019). Thus, this fragment can be used as an alternative target for subunit vaccine development. Despite their ability to ind